National Invasive Alien Plant Survey

National Invasive Alien Plant Survey
Ian J.D.F. Kotzé¹, B. Hein Beukes¹,Terry S. Newby¹, Elna C. Van den Berg¹
¹ARC-Institute for Soil, Climate and Water, Private Bag X5017, Stellenbosch, 7599, South Africa *

The negative impact of Invasive Alien Plant (IAP) species on natural areas, but also on areas such as agricultural land has been extensively researched. Certain mitigation strategies and programmes have been put in place such as the internationally recognized Working for Water Programme. Such an initiative requires objectively determined spatial distribution data of IAP species at the required scale to allow for effective planning, implementation and future monitoring of IAP distribution changes.

The National Invasive Alien Plant Survey project was initiated by the Working for Water Programme and implemented by the Agricultural Research Council. The project objectives are to establish and implement a cost effective, objective and statistically sound IAP monitoring system for South Africa at a quaternary catchment level.

A complete inventory and a standard sampling approach, both have limitations, mainly due to the size of the study area (123 million hectares), variation in the natural environment and therefore the associated costs. An innovative sampling approach was required to meet the project aims. Sampling orientated along an environmentally variable gradient, that contributes the most to species occurrence, would detect the maximum variation in an area, therefore resulting in a stratified proportional sampling approach. A further riparian sample layer was allocated. A third regular grid point layer was created for selected quaternary catchments to serve as an independent source of verification.  Different field survey approaches were simulated and the most suitable was an aerial approach. An extensive field survey was conducted of the sample points. Field data was analyzed and the relevant IAP maps were produced.